172 S C I E N C Z , [VOL.III., NO. 54.

of t!e tlie ti111c recjuirerl by tlrc Prolit of ;t ray iri mov- ing fro111 11 to 1 1 1 , or cice versa. 1)nriilg tlie first inter- val let :E a ~ i dz' alone be open. 'L'bc, rays betrvee~l tllc screens at ttla coliclnsioi~ of tlie first inte!,x7al are sl~omil in the first diagr:tm. During tlre secolrcl in- terval let y alone be open, and let, the reflector at y' send the ray inlpingiiig on i t to\~~itrds 'Flie situatioii z. of the rays at the end of the secor~d interval are sllowu in the secorid diagram. During tlie tliircl ititerval let s' arid z alone be open. Tlre rays between tlie bcreens : ~ ttlie ei~rl of this interval are represt~iited in the t,hit.d diagram. During tlie fourth ititerral let y' alone be ogc~r, and let the reflector at y scbnd the ray frorl~ that poiiit tomartl 2'. 'rlie next interval is n rel~rt,ition(if the first, and so on.

I t is seen thilt, in fact, tlie cliffereace ill the tlirec- tiorls of tile t?vo rays arriving at L' can be made less than any asa~giied finite angle, however s~rlall, by s~tficieiitly iiicreasiiig Ihe distance between the screens, or sufficiently ilecreasing tlic space behveen the openings, or I~otll.

I t is possible that the above process Itlay, from its cornparativa siml~licity, conduce to a clearer i~ntler- standiiig of the relations involved, tliougl~ it seeills inferior to the one originally proposeti irr soirle im- ~ ~ o r t a n t I{. T. EIJT)Y.particulars.

Urliversity of Cincintlati, R P ~ .2, 1834.

The Greely relief expedition. I n view of the cc>ninlent up011 t l ~ e Greely relief es-

pt?ditiori, it Inny not. 1)c: ont of p1ai.c a t this early (late to call atterltio~l to a neglected prir~ciple of arctic ~iavigatiorl wllicll bears wit11 full force irpon the lravigatiorl of the route irl cjuestioli. To its adoption may be traced tlie succcss of' K:~res wit11 tl?i+ Alert and Discovery, ; ~ u d of Sorrlensliiiild will1 t,l~a Vcga; to its neglect, tllc mrecli of tilt? .Je:t~~nette :inti 1 1 1 ( ~I'ro--teus arnong a. l i o s ~of otlrcrs.

Simply stn,tecl, i l is, ~ulder a!l circiuristarices, lo cling to the coast, and anloug its islands firlti protei:- tion against tilo floating ice. To coast along t l ~ c otlgy of the floe, ant1 fo1lo.r~ the opciii~igs i t offers, is a rrrl- tabie siren. Of coursc, tlie principle is llol appiica-. ble till after Jones's Sonntl is l~nssetl; bu.t here tllc course is n s i~a l l j~ free.

roadside, 1 noticetl near Broill~eatl, Wis., a peculiar p l~er~on~enon, TIICnrlliclr rrlay he mortli recording. mud, del~ositetl only a few Ilours before, was still vcrg inobile, and, at tlie point wllere best seeil, cov- eretl an area a rod or niore wide and tlrree or four lorig, preseiititig a pei.fectly plane slmfuce. The steady force of tlie stroiig xvilld mas iiiterr~lljted by occasional gusts of greater ~ i o l e ~ i c e , each of wl~iclt raisecl on the plastic nrnd-surface corritgations, ~vliicli, ill every detail that conlcl be caught during tlieir momentary existence, resembled ripple-niarlrs formeti by water, being a beautiful ant1 distinct series of ~~arnl le lridges slightly concave ton~arcl the ilirection of the mo~~lcling-force. The outlines of thc.se aeoliarl ril~plcs mere no soolier delirred than they began to dissolve, anrl a niinitte or tmo sufficed to obliterate 2~11 trace of thern. Tlie plrenomenon was observed several tirnes on 1,lie sanle surface, arid also in a(1.j:~- cent localities, where tht: consistence of the mud, and therefore the duration of the ridges, varied sligl~tly. The ripples were best defined irl tlre thinnest rnu(1, t l ~ o n g l ~this was nlost favorably situated for tlieir prodilction; ant1 they disappeared less rapidly where formed in 1,lie Inore viscous ~naterial.

This, of coi~rse, is ni)t a ratlically ne\\- phenoiiie- non, but a rare phase of the familiar action of vvi~ltl on liqi~iil surfaces. R. I>. S~r,rsnrrrtu.

Winchell's 'World-life.' \Yill yo11 i)er~i~il ; ~ u eto anuounce that a. number of

errztta, attrib~tl~able to autlror and proof-reader, bol,l~ linve found tlieir way into niy late work on ' IVorltl-. life; ' and I will be glail to mail slilrs of corrections to nrly mlio will liintl1,y ~loti iy Ine by siml~le postal- card that tllcy so tlesirc.:?

11 T,14;XAXI)ER ? ~ T ~ ~ t , ' ~ ~ l z ~ ~ . AUII.l~.i,or,hlicll.

'L'ri~, rr~atcrial circulnstances riilcler whicli scientific discovery IS prosecutecl llnve been complctcly ie~olutioniaed cli~riag the last forly

The 1':skil;lo line~v 111e as 8 X > ir ,!~oinrnr~~tr.,I ears. Of the immense cliangcs that hnvc oc- Xew Havel~, Conn., Vclr. 2 .

The red skies.

I have only t i ~ n e to-day to roply vcry briruv to yoirr eclitorial inquiry on 1). 30, as t,o previons instances of reii skies and v6lcaliic cruptiotis.

You will find a TT'e-t Intlia. iiistance ill IS31 on p. 165 of tlie &teo,.ologicnl li~ii!/irziize for lSP2; bnt the most striking parallel has i~eon poi~itctl out by pro- fessor l<arstrn of Xiel as occurring in 1783. lastir~g about, four molltl~s, i~nd sprc,:ldir~:; over t11c wl101e of li:urope, iiortlier~i Africa, ant1 eastern as is^.

Arrangemorits are being iriarle for tlie conce~ltratiori of all colleclible inforn1:ition tu)oll tile subject, arid 1 sl~niibe prond to act as t ~ i c recei7-er of copies of ally notes or records wllicl~ your rcztlers rusy inl.r~!st to me. G. ,I. h u a r o ~ s ,F.E.S.

62 Camdcli Y q . , I,ondoii, S.\\'., Jan. 25 , l S Y 4 .

/TVe sliall publish I'rofeswr iC,trsIel~'i article liest week.]

Aeolian ripple-marlrs.

On t l ~ ~evening of June 11, 3883, after ,L severe rain-storm, t lu~ing which larqe rluantities of so11 were washed from adjacent ficlrls and tleposited :dong tlie

clirrecl, the majority have fallell ~vi th i~i the last fifteen, one might nlrnost say dohen, years. 11 is interesting aiid profitable to contr:~st the pnst n-it11 tlie present in this respect.

Forts- 5 eayr ago there were very fen.. rno1.t. piol~clrlj no lal~orntolies ~ ~ l i i c h of.i\ c to-t1:lj nonld co~lsicler even tolerable. S o w every univcisity of iiliporta~~ce arid high repute. t l i ~ noilil o\ el,. Ilur l n ~ g e suites of roonis for encl~ clepa~tment of scicnce, ancl oftell ilnmeroos great bnilcliirgs witliin whose m:llls tliousantls n~rd tllousnncls of stnilcuts arc daily k~rought face to face nltlr the ikcts nntl 1:tms of nntr~re. 'rhc ge1ier:ttion t1i:lt is non- gone pursued its scieiltific strrclics ill i~icommodious qruritei.~, aacl eTen those were clestinecl for the use oi' tllc professors rather tllan the students. i71n1q a sm:lll, clingy, and ill-lighted roo111 is still to be seen, where S O I I ~ Cill~istrio~lsS U C C O L ~created new kno~vleclge,-- a s~nall squareclinn~bcr,wit11 crookccl walls, lorn ceiling, unclolating floor,